FCM.subscribeTo not working on iOS

**Describe the bug**
The app is not subscribing to any topic on iOS devices. There is no issue with Android devices.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a new ionic project (6/7)
2. Add Capacitor 5 (iOS)
3. Complete the Ionic Post Notification setup steps
4. Subscribe to a topic using capacitor-community/fcm

**Expected behavior**
The app should subscribe to the topics on iOS just like Android.

**Code**
```
import { Component } from '@angular/core';
import { Router } from '@angular/router';
import { ActionPerformed, PushNotificationSchema, PushNotifications, Token } from '@capacitor/push-notifications';
import { Preferences } from '@capacitor/preferences';
import { FCM } from '@capacitor-community/fcm';

interface SubscriptionPreferences {
[key: string]: boolean;
}

@Component({
selector: 'app-root',
templateUrl: 'app.component.html',
styleUrls: ['app.component.scss'],
})
export class AppComponent {

subscriptionPreferences: SubscriptionPreferences = {};
topics = ['Announcements', 'Calendar', 'Upcoming-Events', 'Block-Rotation', 'Clubs', 'Sports', 'Cafeteria', 'Contests', 'University-Advising', 'New-Student-Help', 'Parent-Info', 'Staff-Directory', 'ios'];

constructor(private router: Router) {}

ngOnInit() {
console.log('Initializing HomePage');

PushNotifications.requestPermissions().then(result => {
if (result.receive === 'granted') {
// Register with Apple / Google to receive push via APNS/FCM
PushNotifications.register();
} else {
// Show some error
}
});

Preferences.get({ key: 'firstTimeOpen' }).then(result => {
const isFirstTimeOpen = result.value;

if (isFirstTimeOpen === null || isFirstTimeOpen === 'true') {
this.topics.forEach(topic => {
FCM.subscribeTo({ topic: topic })
.then(() => {
console.log(`Subscribed to topic ${topic}`);
this.subscriptionPreferences[topic] = true;
Preferences.set({ key: 'firstTimeOpen', value: 'true' });
})
.catch((error) => {
Preferences.set({ key: 'firstTimeOpen', value: 'false' });
});
});

this.subscriptionPreferences = this.topics.reduce((acc: SubscriptionPreferences, topic: string) => {
acc[topic] = true;
return acc;
}, {});

Preferences.set({ key: 'subscriptionPreferences', value: JSON.stringify(this.subscriptionPreferences) });
}
Preferences.get({ key: 'subscriptionPreferences' }).then(result => {
const preferencesValue = result.value;
this.subscriptionPreferences = preferencesValue ? JSON.parse(preferencesValue) : {};
});
console.log(this.subscriptionPreferences)

});

PushNotifications.addListener('registration', (token: Token) => {
console.log('Push registration success, token: ' + token.value);
});

PushNotifications.addListener('registrationError', (error: any) => {
console.log('Error on registration: ' + JSON.stringify(error));
});

PushNotifications.addListener(
'pushNotificationReceived',
(notification: PushNotificationSchema) => {
alert('Notification received: ' + notification.title + '\n' + notification.body);
},
);

PushNotifications.addListener(
'pushNotificationActionPerformed',
(notification: ActionPerformed) => {
console.log('Push action performed: ' + JSON.stringify(notification));

if (notification.notification) {
const notificationData = notification.notification.data;
if (notificationData && notificationData.page) {
this.router.navigateByUrl(notificationData.page);
}
}
},
);
}

}

```

Start by reproducing the issue in a new Ionic 6/7 project with Capacitor 5 on iOS, using the inline AppComponent example and its FCM.subscribeTo calls. Compare the iOS behavior with Android and trace the plugin entry point used by subscribeTo; done means topic subscription succeeds on iOS as well as Android and the reproduction steps no longer fail.

Written by the indexing model from the issue text.